The present invention relates to apparatus for manipulating stacks of sheets or leaves (hereinafter called leaves) which consist of paper, metallic foil, cardboard, plastic foil or the like. More particularly, the invention relates to improvements in apparatus for manipulation of stacks which consist of perforated leaves and wherein the perforations of neighboring leaves at least partially overlap each other to form holes which extend from the one to the other side of the stack. Still more particularly, the invention relates to improvements in apparatus for manipulating stacks of overlapping leaves for the purpose of converting originally straight or inclined holes in one marginal portion of the stack into arcuate passages for convenient introduction of binders, such as spiral binders of the type customarily found in many types of steno pads, exercise books or like stationery products.
It is already known to change the configuration of holes in one marginal portion of each of a series of stacked leaves in order to facilitate the introduction of binders, either in the form of spirals or in the form of C-shaped prongs which are thereupon converted into rings. In many instances, the conversion of straight holes into arcuate passages whose curvature and/or lead resembles the curvature and/or lead of portions of binders is effected by resorting to mandrels which are introduced into the holes and are thereupon pivoted to change the configuration of the holes. It is also known to resort to a shaping member and to means for urging the shaping member against that end face of the stack which is nearest to the row of holes in order to change the shape of the end face by shifting the leaves of the stack relative to each other and by thus changing the configuration of previously straight holes. Reference may be had, for example, to German Pat. No. 1,817,815 which discloses an apparatus with two rows of mandrels. Each mandrel is of arcuate shape and its curvature matches that of the convolutions of a spiral binder. Moreover, the mandrels are inclined in such a way that their inclination matches or approximates the lead of convolutions forming part of a spiral binder which is to be introduced into the deformed holes or passages of the stack. The apparatus comprises means for effecting coarse conformance of originally straight holes to the curvature and lead of convolutions of a spiral binder; this is achieved by resorting to suitable shaping and guide members. In the next step, the arcuate mandrels are caused to penetrate into the partially deformed holes, and the adjacent edge face of the stack is deformed by the shaping member which causes the leaves to move relative to each other so as to achieve a more accurate conformance of the holes or passages to the curvature and lead to the mandrels.
The shifting of leaves for the purpose of conforming the configuration of holes or passages to the lead of convolutions which form part of a spiral binder is relatively simple and can be readily achieved during transport of a stack and/or by resorting to appropriate orienting means at the station where the stacks are assembled. However, conversion of the thus partially deformed or oriented holes into passages whose curvature matches that of a convolution in a spiral binder presents greater problems and takes up more time. The problems are especially acute if the stack is relatively thick, i.e., if the stack comprises a large number of leaves and/or if some or all of the leaves are rather thick. The aforementioned German Pat. No. 1,817,185 purposes to effect preliminary or coarse changes in the configuration of holes to approximate the curvature of the convolutions by resorting to a shaping member which applies sudden or abrupt impulses to a selected portion of the stack or by effecting vibratory movements of the shaping member. It has been found that such vibratory or pulse-like movements of the shaping member do not suffice to effect adequate coarse approximation of the curvature of originally straight holes (or of holes whose inclination matches or approximates the lead of a spiral binder) to the curvature of a convolution, especially if the stack is rather thick. Moreover, the just discussed teaching of German Pat. No. 1,817,815 is unsatisfactory on the additional ground that it takes up too much time to convert the originally straight holes into passages whose curvature and lead match the corresponding characteristics of convolutions which form part of a spiral binder. This is due to the fact that the final or precise adjustment or shifting of leaves so as to impart to the holes a desired optimum (arcuate) shape takes place in two successive stages or steps, i.e., coarse orientation must precede the final orientation of leaves relative to each other. The adjustment is carried out at two successive stations or in two successive stages at one and the same station. In either event, the interval of time which is spent for the conversion of originally straight holes into arcuate passages whose curvature matches that of the convolutions and whose lead matches the lead of the convolutions forming part of a spiral binder is quite long so that the changes in configuration of the holes necessitates a reduction in the output of the machine wherein the stacks are treated for the purpose of being converted or assembled into pads or like stationary products. Otherwise stated, the apparatus for converting originally straight holes into arcuate holes of appropriate curvature and lead constitutes a bottleneck in the machine or production line wherein sheets of paper or the like are assembled into stacks and the stacks are assembled with binders to form note books, pads, exercise books or the like. The provision of two successive stations at the first of which the holes are subjected to coarse treatment and at the second of which the holes are oriented with the aid of aforementioned arcuate mandrels is more satisfactory insofar as the time element is concerned because a stack can be subjected to a secondary or final treatment at the second station while the next-following stack is subjected to a preliminary treatment at the preceding station; however, the provision of two discrete stations contributes to the bulk, initial and maintenance cost of the machine wherein the apparatus for converting originally straight holes in stacks of paper leaves or the like into arcuate holes or passages of appropriate lead is put to use.